Its projections suggest that production of rice, corn and wheat could fall by 10% by 2030, and by up to 37% during the second half of the century.

"If we do not take action, climate change will seriously damage China's long-term grain security," the assessment concludes.

But the report, compiled by more than 10 government bodies including the ministries of foreign affairs and science and technology, stops short of recommending cuts in China's greenhouse gas output.

It confirms the government's long-held view that climate change is caused predominantly by western nations which must cut emissions first.

This view is endorsed in the UN climate convention and Kyoto Protocol, which acknowledge that responsibility for action falls principally on wealthy industrialised nations with high per-capita incomes and emissions.

During his visit to Japan earlier this month, Chinese Prime Minister Wen Jiabao signed an accord with his counterpart Shinzo Abe pledging to work together for a successor to the Kyoto treaty, whose current targets expire in 2012.

But it is not clear what sort of commitments China envisages for itself and other developing countries in such a pact.